Biophysical properties of bovine cervical mucus have been defined, and new methods of measurement have been developed and applied to mucus collected throughout the estrous cycle. Pulsed-gradient nuclear magnetic resonance spectroscopy (NMR) and mucous plasma expression techniques have been applied in conjunction with mathematical modeling to study quantitatively the macromolecular mucous architecture. Viscoelastic properties of the mucus have been studied using new instruments specifically designed for this purpose. The NMR investigation utilized the Carr-Purcell pulse sequence to study the self diffusion constant (D) of H2O molecules within bovine mucus. Measurements of D show that water molecules are highly mobile in mucus. The rheological properties of mucus are therefore strongly dependent upon the size of particle/molecule utilized for the measurement.